Comment by cubefox
8 hours ago
In case of many textures (grass, sand, hair, skin etc) it makes little difference whether the high frequency details are reproduced exactly or hallucinated. E.g. it doesn't matter whether the 1262nd blade of grass from the left side is bending to the left or to the right.
And in the case of many others, it makes a very significant difference. And a codec doesn't have enough information to know.
Imagine a criminal investigation. A witness happened to take a video as the perpetrator did the crime. In the video, you can clearly see a recognizable detail on the perpetrator's body in high quality; a birthmark perhaps. This rules out the main suspect -- but can we trust that the birthmark actually exists and isn't hallucinated? Would a non-AI codec have just showed a clearly compression-artifact-looking blob of pixels which can't be determined one way or the other? Or would a non-AI codec have contained actual image data of the birth mark in sufficient detail?
Using AI to introduce realistic-looking details where there was none before (which is what your proposed AI codec inherently does) should never happen automatically.
> And in the case of many others, it makes a very significant difference.
This is very true, but we're talking about an entertainment provider's choice of codec for streaming to millions of subscribers.
A security recording device's choice of codec ought to be very different, perhaps even regulated to exclude codecs which could "hallucinate" high-definition detail not present in the raw camera data, and the limitations of the recording media need to be understood by law enforcement. We've had similar problems since the introduction of tape recorders, VHS and so on, they always need to be worked out. Even the phantom of Helibronn (https://en.wikipedia.org/wiki/Phantom_of_Heilbronn) turned out to be DNA contamination of swabs by someone who worked for the swab manufacturer.
I don't understand why it needs to be a part of the codec. Can't Netflix use relatively low bitrate/resolution AV1 and then use AI to upscale or add back detail in the player? Why is this something we want to do in the codec and therefore set in stone with standard bodies and hardware implementations?
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There’s an infamous case of xerox photocopiers substituting in incorrect characters due to a poorly tuned compression algorithm. No AI necessary.
https://en.wikipedia.org/wiki/JBIG2#:~:text=Character%20subs...
Yeah, I had that case in mind actually. It's a perfect illustration of why compression artifacts should be obvious and not just realistic-looking hallucinations.
> a codec doesn't have enough information to know.
The material belief is that modern trained neural network methods that improve on ten generations of variations of the discrete cosine transform and wavelets, can bring a codec from "1% of knowing" to "5% of knowing". This is broadly useful. The level of abstraction does not need to be "The AI told the decoder to put a finger here", it may be "The AI told the decoder how to terminate the wrinkle on a finger here". An AI detail overlay. As we go from 1080p to 4K to 8K and beyond we care less and less about individual small-scale details being 100% correct, and there are representative elements that existing techniques are just really bad at squeezing into higher compression ratios.
I don't claim that it's ideal, and the initial results left a lot to be desired in gaming (where latency and prediction is a Hard Problem), but AI upscaling is already routinely used for scene rips of older videos (from the VHS Age or the DVD Age), and it's clearly going to happen inside of a codec sooner or later.
I'm not saying it's not going to happen. I'm saying it's a terrible idea.
AI upscaling built in to video players isn't a problem, as long as you can view the source data by disabling AI upscaling. The human is in control.
AI upscaling and detail hallucination built in to video codecs is a problem.
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Maybe there could be a "hallucination rate" parameter in the encoder: More hallucination would enable higher subjective image quality without increased accuracy. It could be used for Netflix streaming, where birthmarks and other forensic details don't matter because it's all just entertainment. Of course the hallucination parameter needs to be hard coded somehow in the output in order to determine its reliability.